Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on semiconductor devices. Insulated Gate Bipolar Transistors (IGBTs) combine isolated gate electrodes for controlling the current with the high-current and low-saturation-voltage capability of bipolar transistors and have thus been used for various applications including but not limited to traction motor control and as switches in power supplies and power converters, in particular for medium- to high-power applications.
Meanwhile, dynamic properties such as switching losses and softness of power semiconductor devices have become more important. Further, the robustness (ruggedness) under high switching speed is often desired to be high. Even further, a degradation of the characteristic blocking curves of power semiconductors is often to be avoided. For power IGBTs and associated free-wheeling diodes for high reverse voltages (blocking voltages) of at least about 3 kV, an n-doped field-stop layer arranged next to a p-doped back-side emitter or cathode region and having a higher dopant concentration than an adjoining n-doped drift or base layer may be provided to reduce switching losses. There are bipolar power semiconductor devices with field-stop layer which have a high switching robustness. However, manufacturing variations may result in less stronger IGBT power devices which are not detected during series tests typically carried out at lower switching speeds. During operation, the less strong IGBTs may cause failure at high switching speeds of more than 108 V/s or more than 109 V/s. Therefore, further improvements with regard to switching robustness of bipolar semiconductor devices at high switching speeds (hard commutating) and suitable manufacturing processes are desired.